The invention relates to a hair roller used for setting hair into a predetermined pattern of curls and waves, by winding strands of hair around the heated cylindrical body. These rollers are heated by being placed on heated metal posts forming part of an electric hair setter unit, which is usually in the form of a metal plate carrying from 5 to 30 posts, each post heating one curler. Upon the rollers reaching the suitable temperature, they are taken off the posts, one by one, and placed into the correct position in a woman's head hair.
The existing rollers comprise a cylindrical hollow body of a thermo-plastic material, provided on its outer surface with a plurality of radial teeth and, optionally, with co-axial rings at one or both ends. The cylindrical hollow portion of the plastics body is provided with a tubular insert which is generally pressed into the body and which is adapted to transfer heat from the heated metal post on which it is placed, to the outer surface of the roller, and to the hair wound around it.
The metal posts of the existing hair setter units are either cylindrical or frusto-conical, and it will be readily understood that the contact area between metal insert and post is only along a line or a narrow strip; in the case of a conical post, contact is along the circular lower edge of the tubular insert, and in the case of a cylindrical post, contact is along a straight longitudinal line on the cylinder surface. Only this small contact area serves to transfer heat by conduction, and most of the heat is, therefore transmitted by convection through interposed air, resulting in rather slow heat transfer. Another drawback of the existing rollers is the frequent loosening of the insert caused by different coefficients of expansion of the metal and the plastics, further reducing heat transfer between these components. A further drawback of the cylindrical insert is frequent wedging or jamming of the roller, but on a cylindrical and a frusto-conical post.
With a view to obviate these drawbacks, it is a primary object of the present invention to provide a hair roller wherein a tubular metal insert is elastically pressed against the inner walls of the plastics curler body. A second object is to provide intimate contact between frusto-conical or conical posts and the insert over a large portion of the entire insert surface. Still another object is to prevent the rollers from wedging on the posts and hindering their ready removal therefrom.